Hashmap in Java | Internal Working of Hashmap in Java | Hashmap Implementation | DSA-One Course #30

Hi guys, In this video, we're going to learn how HashMap works internally.
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[@amitanand3672]

Few other questions I have come across which everyone should prepare beforehand: 1. What is bucketing in hashmap ? 2. What is loadfactor ? 3. Why hashmap is not recommended in a multi threaded environment ? 4. Implement a hashmap using custom class as key 5. is it mandatary to override equals and hashcode method ? What will happen if not overridden ? 6. What is the difference between hashmap and concurrent hashmap also explain the working of concurrent hashmap .

[@mohammadfaizanhashmi4213]

thanx a lot bro, bohot bohot shukriya bhaijan,,,maine noten kr lia hai

[@frankfernandes718]

woh jo table tha red me 9:57 woh bucket hai

[@pankajchaudhari2413]

Bucketing is nothing but index of that node Array Hashmap doesn't contain synchronized method or variable , that's y it is not thread safe, overcome to resolve this problem we are having HashTable (as it contains all synchronized method)

[@Basukinathkr]

Great Amit. For people who are looking here for the answers - Buckets are basically the area that contains values. Loadfactor is the threshold for the percentage of the bucket when it is decided that now bucket is going to be full and then the capacity is doubled. By default, loadfactor is 75% and capacity is 16. Totally configurable via constructor. The reason a hashmap isn't recommended in a MT env because when multiple threads start to access the data while some thread is updating it, there can be issues. Whenever overriding equals, it is mandatory to override hashCode so that every time when equals is called, the values generated by hashCode remain consistent. Rest 4 and 6 are explanatory. Can be looked on internet. Easy stuff.

[@nitishprasadkushwaha]

Bucketing in HashMap is the process of storing multiple values in a single location (bucket) of the internal array of the HashMap, which is indexed using a hash function. The hash function calculates the hash code of the key and uses it as an index in the array. If multiple keys have the same hash code, they are stored in the same bucket as linked nodes. Load factor is a measure of how full a HashMap is allowed to get before its capacity is automatically increased. It is a float value that ranges from 0.0 to 1.0. When the number of entries in the HashMap exceeds the load factor multiplied by the current capacity, the capacity is increased, and the entries are rehashed. HashMap is not recommended in a multi-threaded environment because it is not thread-safe. If multiple threads access a HashMap concurrently, it may result in an inconsistent state of the HashMap, leading to data loss or unexpected results. ConcurrentHashMap is recommended for use in a multi-threaded environment. Here's an example implementation of a HashMap using a custom class as a key: class Person { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } // getters and setters @Override public int hashCode() { return Objects.hash(name, age); } @Override public boolean equals(Object o) { if (this == o) return true; if (!(o instanceof Person)) return false; Person person = (Person) o; return age == person.age && Objects.equals(name, person.name); } } class CustomHashMap { private List[] buckets; private int capacity; private int size; private static class Entry { K key; V value; public Entry(K key, V value) { this.key = key; this.value = value; } // getters and setters } public CustomHashMap(int capacity) { this.buckets = new List[capacity]; this.capacity = capacity; this.size = 0; } public void put(K key, V value) { int index = key.hashCode() % capacity; if (buckets[index] == null) { buckets[index] = new LinkedList(); } for (Entry entry : buckets[index]) { if (entry.key.equals(key)) { entry.value = value; return; } } buckets[index].add(new Entry(key, value)); size++; } public V get(K key) { int index = key.hashCode() % capacity; if (buckets[index] == null) { return null; } for (Entry entry : buckets[index]) { if (entry.key.equals(key)) { return entry.value; } } return null; } public int size() { return size; } // other methods } It is highly recommended to override the equals() and hashCode() methods when using custom objects as keys in a HashMap. If these methods are not overridden, the default implementations in the Object class are used, which compares object references rather than object contents. This can lead to unexpected behavior, where two objects that are considered equal by their contents are not considered equal by the HashMap. As a result, the HashMap may not be able to retrieve the values correctly.

[@DensonGeorge18]

I am not a beginner. I still find the DSA 1 series very helpful to revise the concepts and learn new things for interviews.

[@nitishprasadkushwaha]

Bucketing in HashMap is the process of storing multiple values in a single location (bucket) of the internal array of the HashMap, which is indexed using a hash function. The hash function calculates the hash code of the key and uses it as an index in the array. If multiple keys have the same hash code, they are stored in the same bucket as linked nodes. Load factor is a measure of how full a HashMap is allowed to get before its capacity is automatically increased. It is a float value that ranges from 0.0 to 1.0. When the number of entries in the HashMap exceeds the load factor multiplied by the current capacity, the capacity is increased, and the entries are rehashed. HashMap is not recommended in a multi-threaded environment because it is not thread-safe. If multiple threads access a HashMap concurrently, it may result in an inconsistent state of the HashMap, leading to data loss or unexpected results. ConcurrentHashMap is recommended for use in a multi-threaded environment. Here's an example implementation of a HashMap using a custom class as a key: class Person { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } // getters and setters @Override public int hashCode() { return Objects.hash(name, age); } @Override public boolean equals(Object o) { if (this == o) return true; if (!(o instanceof Person)) return false; Person person = (Person) o; return age == person.age && Objects.equals(name, person.name); } } class CustomHashMap { private List[] buckets; private int capacity; private int size; private static class Entry { K key; V value; public Entry(K key, V value) { this.key = key; this.value = value; } // getters and setters } public CustomHashMap(int capacity) { this.buckets = new List[capacity]; this.capacity = capacity; this.size = 0; } public void put(K key, V value) { int index = key.hashCode() % capacity; if (buckets[index] == null) { buckets[index] = new LinkedList(); } for (Entry entry : buckets[index]) { if (entry.key.equals(key)) { entry.value = value; return; } } buckets[index].add(new Entry(key, value)); size++; } public V get(K key) { int index = key.hashCode() % capacity; if (buckets[index] == null) { return null; } for (Entry entry : buckets[index]) { if (entry.key.equals(key)) { return entry.value; } } return null; } public int size() { return size; } // other methods } It is highly recommended to override the equals() and hashCode() methods when using custom objects as keys in a HashMap. If these methods are not overridden, the default implementations in the Object class are used, which compares object references rather than object contents. This can lead to unexpected behavior, where two objects that are considered equal by their contents are not considered equal by the HashMap. As a result, the HashMap may not be able to retrieve the values correctly.

[@tech_wizard9315]

Please add questions for every video of DSA course which would be enough to crack tech giant's for beginners

[@mousumi721]

Thank you bhaiya for this series🌸.i'm really grateful.

[@GuruPrasadShukla]

best video on hashmaps in whole coder community!

[@8750795655]

Great, very well and easily explained

[@anujpotdar3529]

I was asked this yesterday, could not answer. I started searching for solutions, most of them were too long and difficult to understand. This one taught the concept very well, keep such awesome videos, and more power to you Anuj!

[@AnujBhaiya]

Thanks Anuj ♥️

[@parthparmar9798]

thanks for the extremely good content and hardwork.

[@unboxingsillystuffs4920]

Thank you Anuj..you explained very well.

[@surajdhotre2889]

U really gr8 bhaiya.Your video hleping me a lots....god bless u 😇

[@ranjeet5806]

Great explanation, really helpful.

[@nitin5865]

Perfectly explained 👍

[@sathishrajasekar1155]

Thank you Anuj, The Video was helpful.

[@tanmoydutta5846]

I was also asked the internal implementation of this in JPMC interview (technical round).

[@ashutoshpandey4171]

Thanks for the effort, anuj bhaiya

[@ShankarKumar-ko8lt]

This video is very Helpful for me Thank you Anuj Bhaiya.

[@rameezkhan2220]

The way of explanation is excellent👌👌👌

[@awwush]

are Abhi aapka hi videos dekhra tha ARRAYS superb!!

[@user-ij9zq9qf8s]

Amazing explanation, thanks man!

[@superbudy8338]

very helpful thanku for making these kind of videos :)

[@acoustic_ng8706]

Very helpful ! Thank you Anuj bhai !

[@shivisharma4267]

Bhaiya please make a video on roadmap to cloud computing🙏🙏🙏

[@antorsaha6065]

Thank you bhaiya for this series. This is most useful dsa series.😍

[@AnujBhaiya]

You're welcome ☺️

[@sumeet115]

Great explanation. Thanks 👍 ..

[@chaitanyaasati]

Yeah, It helped to understand the concept.

[@itz_me_imraan02]

The videos are too gud... Plz try to maintain consistency in DSA course🙏🙏...

[@itsShashwat]

Great video @Anuj Bhaiya

[@nandiniverma5273]

It was helpful , Thankyou for deep Knowledge

[@shashwatmishra7056]

A guy from Amazon Seattle, Washington, interviewed me today asked me the same concept

[@chetantailor3620]

Another worth 16 minutes 👌💫

[@CodeCult413]

Excellent explanation bhai. Bhai, on which basis an initial length of hash table get decided?? Is it same like an internal working of arraylist for initial length of hashtable or something else?? And bhai, please increase the frequency of videos on DSA-ONE. I'm eagerly waiting for upcoming videos.

[@PAWANKUMAR-el2zk]

Bhaiya make more such kind of videos on all collection's or tree👍🏻

[@nishantaggarwal830]

It was very interesting and helpful

[@vishaldas5692]

Yes it was helpful btw plzz make a video on how to convert that linked list into bst in hashed map as u said is done in Java 8..🙃❣️

[@stith_pragya]

Thank You So Much bhaiya,............🙏🙏🙏

[@dharmeshkhasiya6737]

Thanks for explaining

[@shubhammahawar6206]

Thanks for explaining.

[@mrityunjoybarman9098]

You always make helpful videos vaiya...

[@devendersinghrathore8837]

Yes. It is really helpful.

[@skelafahmed]

Yes bhaiya its really helpful thank you 😀

[@gmanikantasai3655]

Awesome explanation brother💯💯

[@vivekshokeen1192]

YES, IT WAS HELPFUL! bhaiya

[@madhusmitamishra7801]

Watched this before 15mins of my interview and interviewer asked the same question. Thank you ☺️.

[@abilashappat9640]

Very helpful indeed

[@nandabawane9117]

No wondor.... Your Videos are always be useful...

[@Vishal-242]

Most clear explanation I have seen

[@AbhayKumar-lb6fl]

Yes, it was helpful.

[@raghavendraraviteja1055]

Thanks, it is helpful

[@sonam3531]

Thanks , it was good information.

[@auroshisray9140]

thanks bhaiya!

[@sandeshtiwaris6829]

Yes, it was helpful

[@thebugger7269]

Sir please make a video on hash mam and concurrent hash map how perform different internally

[@ashapilkhwal6320]

Awesome content and presentation

[@adityadev2825]

Yes the videos was very helpful

[@ramgopalbhajans3982]

Yes it was helpful.

[@user-gk7xb6bp7c]

YES, IT WAS HELPFUL

[@gurkiratkaur4087]

Very helpful

[@surajwaghmare4653]

Very Helpful

[@AhamedKabeer-wn1jb]

Thank you Bhaiya..

[@shriduttpatel1350]

Thank you @Anuj bhaia. It was really help full. Please do not stop making videos like this😀.

[@AnujBhaiya]

If it was really helpful, I will never stop making videos like this 🤗

[@surajchavan1000]

Yes, very helpful

[@learntocode8000]

Yes, It was Helpful

[@jainikprajapati1632]

Yes it is useful 👍 thanks 😀

[@av98]

Helpful

[@ashwithchandra2622]

thanks bhayya nice explanation😘

[@anshukumari6616]

Yes, it was useful.

[@mruduladdipalli5417]

EK Number Bhai

[@StudyiMnimal1743]

great bhaiya

[@rrtt6903]

yes, it was helpful

[@venkatasaikrishnamarri1158]

perfect tutorial

[@shreyanshgupta8959]

Yes it was Helpful

[@sumitrana2628]

Very helpful 🙂👍🏻

[@kashisharora1018]

Very nice explanation

[@factsEcho--]

Yes video was helpful 🙂🙂

[@agyaani8060]

Thankuu so much bhaiya❤❤

[@harshitsrivastava9903]

Thanks a lot !!

[@swayam2367]

thanks bhai...👍👍

[@nileshmutthe5457]

This was helpful

[@anupamdubey5736]

😯😯Where's that CAP/BEANIE! Loved the explanation!!❤❤

[@rahulshinde6648]

Thank you

[@indranilmetiya6972]

Yes it was helpful

[@deev1032]

very helpful

[@debasispaul4410]

it was helpful

[@surajwaghmare4653]

Yes It was useful

[@tejasbavkar2811]

thank you..

[@pratikjha2742]

yes it was helpful

[@vaibhavsomani5161]

Hash Code is basically the Memory Reference of that object so what is need for doing the hashing by Modulo and all.

[@codehustler8582]

YES IT HELPS

[@rahulsrivastava1040]

Anuj bhaiya op❣️❣️

[@ankitdubey6813]

This series is the most useful ❤

[@piyushkesharwani1987]

Great one, Please make a video on the Internal working of "HEAP" also.

[@amanrai8010]

Thanks

[@rajanwalia4tech]

I didn't knew about that java8 implement hashmap using self balancing BST. Yes video was helpful.

[@meetsoni1938]

Yes it is helpful 😃

[@codingwithadesh6935]

Osm❤️

[@pareeks]

Great video. Two things TBC: 1. New values are pre-appended, not appended at end. 2. In case of collision in get(Key), value is not checked for equals() but key is checked.

[@RupeshYadav-kt5dv]

Good job 👏 👍 👌

[@anuj5927]

Yes it was helpful :)

[@abhinavmishra7617]

helpful